The present invention relates to the construction of grammars used in speech recognition. In particular, the invention relates to the construction of grammars that include semantic tags.
In speech recognition systems, a computer system attempts to identify a sequence of words from a speech signal. One way to improve the accuracy of the recognition is to limit the recognition to a set of selected phrases. This is typically done by limiting valid recognition hypothesis to phrases that are found in a context-free grammar (CFG).
In some speech recognition systems, the context-free grammar is augmented by associating semantic tags and their corresponding values to words or phrases in the grammar. With such augmented systems, the semantic information is returned to an application along with the recognized phrase. This allows the application to take action based on the semantic information without having to first translate the recognition of the phrase into some semantic value.
In prior art systems, the semantic tag and value are only passed to the application after a complete utterance has been recognized. However, the semantic meaning of the utterance may be apparent earlier in the utterance. Since the recognition engine identifies the end of an utterance by detecting some period of silence, at a minimum, the user must wait through the silence period before the application takes action on the speech signal.
This delay is perceivable and annoying to users. As such, a speech recognition system is needed that allows applications to take actions before an utterance has been completely recognized.